When pyroelectric ceramic compositions absorb infrared radiation energy and undergo changes in temperature, charges are formed on surfaces by changes in the spontaneous polarization. Pyroelectric ceramic compositions are widely used in pyroelectric bodies for pyroelectric elements by utilizing this property and are applied to infrared detectors.
This type of pyroelectric ceramic compositions is required to have a high pyroelectric property, i.e., required to change the spontaneous polarization with changes in temperature of pyroelectric bodies. Moreover, a pyroelectric body having an excessively low relative dielectric constant is easily affected by stray capacitance of an external circuit of an infrared detector and thus generates large noise. In contrast, a pyroelectric body having an excessively high relative dielectric constant has decreased detectivity since surface charges (pyroelectric charges) generated on the surface of a pyroelectric element are accumulated in the element itself. Thus, the pyroelectric ceramic composition is required to have an adequate level of relative dielectric constant.
For example, Patent Document 1 proposes use of a pyroelectric ceramic composition in the pyroelectric element, the composition containing a lead titanate (PT) compound represented by general formula: (Pb1−xCax){(Ni1/3Nb2/3)yTi1−y}O3 (wherein x and y satisfy 0.25≦x≦0.35 and 0.01≦y≦0.06) as the main component and 0.3 to 2.5 at % Mn as an auxiliary component.
In Patent Document 1, part of Pb, which is an A site component of a perovskite crystal structure (general formula: ABO3), is replaced with Ca in the range of 25 to 35 mol % so as to achieve a target optimum relative dielectric constant. Moreover, in Patent Document 1, part of Ti, which is a B site component, is replaced with (Ni1/3Nb2/3) to improve the pyroelectric property, and a particular amount of Mn as the auxiliary component is contained to improve the sinterability.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 1-261876